Wireless access network node having an off state

ABSTRACT

A wireless access network node receives a configuration for a discovery signal for transmission by the wireless access network when in an off state. The wireless access network node in the off state transmits the discovery signal according to the configuration for detection by a user equipment (UE).

BACKGROUND

As the demand for wireless data communication using wireless userequipments (UEs) has increased, wireless access service providers areincreasingly facing challenges in meeting capacity demands in regionswhere the density of users is relatively high. To address capacityissues, deployment of small cells has been proposed. A small cell (ormultiple small cells) can operate within a coverage area of a largercell, referred to as a macro cell. A small cell has a coverage area thatis smaller than the coverage area of the macro cell.

If small cells are deployed, then communications with UEs can beoffloaded from the macro cell to the small cells. In this way, datacommunication capacity is increased to better meet data communicationdemands in regions of relatively high densities of UEs.

SUMMARY

In general, according to some implementations, a wireless access networknode receives a information relating to a configuration of a discoverysignal for transmission by the wireless access network when in an offstate. The wireless access network node in the off state transmits thediscovery signal according to the configuration for detection by a userequipment (UE).

In general, according to further implementations, a wireless accessnetwork node receives information relating to a configuration of anuplink signal of a user equipment (UE) to enable the wireless accessnetwork node to monitor the uplink signal while the wireless accessnetwork node is in an off state.

In general, according to other implementations, a first wireless accessnetwork node sends, to a user equipment (UE), a Radio Resource Control(RRC) message containing timing information pertaining to a discoverysignal to be transmitted by a second wireless access network node in anoff state.

In general, according to additional implementations, a first wirelessaccess network node sends, to a second wireless access network node,information relating to a configuration of an uplink signal of a userequipment (UE) to be measured by the second wireless access network nodein an off state.

Other or alternative features will become apparent from the followingdescription, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments are described with respect to the following figures.

FIG. 1 is a schematic diagram of an example network arrangement thatincludes macro cells and small cells, in accordance with someimplementations.

FIG. 2 is a flow diagram of a process for transmitting a discoverysignal by a sleeping small cell wireless access network node, accordingto some implementations.

FIG. 3 is a schematic diagram of transmissions by an active wirelessaccess network node and a sleeping wireless access network node,according to some implementations.

FIG. 4 is a schematic diagram of transmissions of primary and seconddiscovery signals, according to further implementations.

FIGS. 5-7 are schematic diagrams of transmissions of discovery signalsin different small cells, according to various implementations.

FIG. 8 is a flow diagram of a process of detecting a nearby userequipment by a sleeping wireless access network node, according to someimplementations.

FIG. 9 is a schematic diagram of detecting a random access signaltransmitted by a user equipment, according to further implementations.

FIG. 10 illustrates mapping between uplink sequences and power levels,according to alternative implementations.

FIG. 11 is a block diagram of a small cell wireless access network nodethat includes various timers for controlling states of the small cellwireless access network node, according to further implementations.

FIG. 12 is a schematic diagram of a collection of subframes that isdivided into first and second sets of subframes, according to furtherimplementations.

FIG. 13 is a block diagram of a computing system according to someimplementations.

DETAILED DESCRIPTION

Small cells are provided by small cell wireless access network nodes. Awireless access network node is responsible for performing wirelesstransmissions and receptions with user equipments (UEs) within acoverage area of the cell provided by the wireless access network node.A coverage area can refer to a region where mobile services can beprovided by a network node to a target level. Examples of UEs caninclude any of the following: smart phones, personal digital assistants,notebook computers, tablet computers, or any other devices that arecapable of wireless communications.

A wireless access network node for a small cell can be considered as alower power wireless access network node. A lower power wireless accessnetwork node transmits signals at a power that is generally lower than apower of a macro wireless access network node. A macro cell provided bya macro wireless access network node has a coverage area that isgenerally larger than the coverage area of a small cell provided by asmall cell wireless access network node.

Examples of small cell wireless access network nodes include picowireless access network nodes, femto wireless access network nodes,relay nodes, and so forth. A pico cell provided by a pico wirelessaccess network node refers to a cell that has a relatively smallcoverage area, such as within a building, a train station, an airport,an aircraft, or other small area. A femto cell provided by a femtowireless access network node is a cell that is designed for use in ahome or small business. A femto cell is associated with a closedsubscriber group (CSG), which specifies that only users within aspecified group are allowed to access the femto cell. A relay node isused for relaying data from one wireless entity to another wirelessentity. There can be other examples of small cell wireless accessnetwork nodes.

An issue associated with providing a relatively large density of smallcells is that increased interference can occur. For example,communications in one cell (referred to as an aggressor cell) caninterfere with communications in another cell (referred to as a victimcell). In some cases, small cells can also overlap with each other incoverage, which can lead to increased interference.

To reduce interference, a small cell wireless access network node can beturned off. Since the small cell wireless access network node that isturned off does not transmit signals or only transmit the signals withreduced density, the small cell wireless access network node that isturned off would cause less or no interference over other nearby smallcells. Additionally, turning off a small cell wireless access networknode can save energy.

In some cases, small cell wireless access network nodes can be turnedoff in specific time intervals, such as during time intervals ofexpected low usage (e.g. during the night). The small cell wirelessaccess network nodes can be turned back on during time intervals ofexpected high usage (e.g. during the daytime hours).

In other cases, a small cell wireless access network node can be turnedon and off more dynamically. For example, a small cell wireless accessnetwork node can be turned on and off more frequently based on detectedtraffic or interference conditions.

A small cell wireless access network node that is in the off state doesnot transmit and receive a majority of signals (including signals forcarrying data and control information) that the small cell wirelessaccess network node would transmit and receive when it is in the onstate. As a result, a small cell wireless access network node that is inthe off state is not able to serve UEs within the coverage area of thesmall cell wireless access network node. Note that a small cell wirelessaccess network node in an off state may still be able to communicatewith a core network node or another wireless access network node.

However, as discussed further below, a small cell wireless accessnetwork node in the off state may still remain capable of transmittingor receiving (or both) selected signal(s), to use for discovery purposesor other purposes.

Note that in some examples, a small cell wireless access network nodecan operate using a number of component carriers, which allows a UE tocommunicate with the wireless access network node using one or multiplecomponent carriers (at respective different frequencies). The componentcarriers can be aggregated together to provide carrier aggregationservice for the UE, in which the UE can establish multiple concurrentwireless connections with the wireless access network node on therespective component carriers.

Each of the component carriers can provide a respective cell. Inexamples where a wireless access network node provides multiplecomponent carriers (multiple cells), turning on or off the wirelessaccess network node can refer to turning on or off of one cell (ormultiple cells) provided by the respective component carriers of thewireless access network node.

When a small cell wireless access network node is turned off, severalissues may arise. First, a UE that is within a coverage area of awireless access network node that is in an off state may not be able todetermine whether or not the UE has entered such coverage area. Second,a wireless access network node that is in an off state may not be ableto determine that a UE has entered the wireless access network node'scoverage area.

Moreover, transitioning a wireless access network node from an on stateto an off state may affect one or more UEs within the coverage area ofthe small cell wireless access network node. In addition, further issuesmay relate to the manner in which a wireless access network node is tobe awakened from an off state to an on state, or to the manner ofdynamically controlling the on/off state of a wireless access networknode.

In the ensuing discussion, reference is made to techniques or mechanismsthat are applied with respect to small cell wireless access networknodes that can be turned on and off. However, in alternativeimplementations, similar techniques or mechanisms can be applied toother types of wireless access network nodes, including macro wirelessaccess network nodes.

Also, reference is made to mobile communications networks that operateaccording to the Long-Term Evolution (LTE) standards as provided by theThird Generation Partnership Project (3GPP). The LTE standards are alsoreferred to as the Evolved Universal Terrestrial Radio Access (E-UTRA)standards. Although reference is made to E-UTRA in the ensuingdiscussion, it is noted that techniques or mechanisms according to someimplementations can be applied to other wireless access technologies.

In an E-UTRA network, a wireless access network node can be implementedas an enhanced Node B (eNB), which includes functionalities of a basestation and base station controller. Thus, in an E-UTRA network, a macrowireless access network node is referred to as a macro eNB. In an E-UTRAnetwork, small cell wireless access network nodes can be referred to assmall cell eNBs.

FIG. 1 illustrates an example arrangement that includes network nodesthat are part of a mobile communications network that supports wirelesscommunications with UEs. A macro cell 102 corresponds to a coverage areaprovided by a macro eNB 104.

In addition, a number of small cells 106 are depicted as being withinthe coverage area of the macro cell 102. Each small cell 106 correspondsto a coverage area provided by a respective small cell eNB 108. One ofthe small cells is labeled 106-1, and the corresponding small cell eNBis labeled 108-1.

A wireless UE 110 within the coverage area of the small cell 106-1 isable to wirelessly communicate with the small cell eNB 108-1. The UE 110is also able to wirelessly communicate with the macro eNB 104. Althoughjust one UE 110 is depicted in FIG. 1, it is noted that multiple UEs maybe present in coverage areas of each of the small cells 106 as well aswithin the coverage area of the macro cell 102.

A first wireless connection 112 can be established between the UE 110and the small cell eNB 108-1. In addition, a second wireless connection114 can be established between the UE 110 and the macro eNB 104. In suchan arrangement, the UE 110 is considered to have established dualconcurrent wireless connections with the macro eNB 104 and the smallcell eNB 108-1. In other examples, the UE 110 can establish multipleconcurrent wireless connections with the macro eNB 104 and with multiplesmall cell eNBs 108.

FIG. 1 also shows a backhaul link 116 between the macro eNB 104 and eachof the small cell eNBs 108. The backhaul link 116 can represent alogical communication link between two nodes; the backhaul link 116 caneither be a direct point-to-point link or can be routed through anothercommunication network or node. In some examples, the backhaul link 116is a wired link. In other examples, the backhaul link 116 is a wirelesslink. Although not shown, backhaul links may also be provided betweensmall cell eNBs 108.

In some implementations, the macro cell 102 (and more specifically themacro eNB 104) can provide all of the control plane functions, while asmall cell 106 (more specifically the corresponding small cell eNB 108)provides at least a portion of the user plane functions for adual-connection capable UE (a UE that is capable of concurrentlyconnecting to both macro and small cells). Note that the macro eNB 104can also provide user plane functions for the dual-connection capableUE.

Control plane functions involve exchanging certain control signalingbetween the macro eNB 104 and the UE 110 to perform specified controltasks, such as any or some combination of the following: networkattachment of a UE, authentication of the UE, setting up radio bearersfor the UE, mobility management to manage mobility of the UE (mobilitymanagement includes at least determining which infrastructure networknodes will create, maintain or drop uplink and downlink connectionscarrying control or user plane information as a UE moves about in ageographic area), performance of a handover decision based on neighborcell measurements sent by the UE, transmission of a paging message tothe UE, broadcasting of system information, control of UE measurementreporting, and so forth. Although examples of control tasks and controlmessages in a control plane are listed above, it is noted that in otherexamples, other types of control messages and control tasks can beprovided. More generally, the control plane can perform call control andconnection control functions, and can provide messaging for setting upcalls or connections, supervising calls or connections, and releasingcalls or connections.

User plane functions relate to communicating traffic data (e.g. voicedata, user data, application data, etc.) between the UE and a wirelessaccess network node. User plane functions can also include exchangingcontrol messages between a wireless access network node and a UEassociated with communicating the traffic data, flow control, errorrecovery, and so forth.

A small cell connection can be added to or removed from a UE under thecontrol of the macro eNB 104. In some implementations, the action ofadding or removing a small cell for a UE can be transparent to a corenetwork 118 of the mobile communications network. The core network 118includes a control node 120 and one or more data gateways 122. The datagateway(s) 122 can be coupled to an external packet data network (PDN)124, such as the Internet, a local area network (LAN), a wide areanetwork (WAN), and so forth.

In an E-UTRA network, the control node 120 in the core network 118 canbe implemented as a mobility management entity (MME). An MME is acontrol node for performing various control tasks associated with anE-UTRA network. For example, the MME can perform idle mode UE trackingand paging, bearer activation and deactivation, selection of a servinggateway (discussed further below) when the UE initially attaches to theE-UTRA network, handover of the UE between macro eNBs, authentication ofa user, generation and allocation of a temporary identity to a UE, andso forth. In other examples, the MME can perform other or alternativetasks.

In an E-UTRA network, the data gateway(s) 122 of the core network 118can include a serving gateway (SGW) and a packet data network gateway(PDN-GW). The SGW routes and forwards traffic data packets of a UEserved by the SGW. The SGW can also act as a mobility anchor for theuser plane during handover procedures. The SGW provides connectivitybetween the UE and the PDN 124. The PDN-GW is the entry and egress pointfor data communicated between a UE in the E-UTRA network and a networkelement coupled to the PDN 124. There can be multiple PDNs andcorresponding PDN-GWs. Moreover, there can be multiple MMEs and SGWs.

Note that a legacy UE (a UE that is not capable of establishing multipleconcurrent wireless connections with both a macro cell and one or moresmall cells) can connect to either a macro cell or a small cell usingtraditional wireless connection techniques.

When a UE moves under the coverage of a small cell 106, the macro eNB104 may decide to offload some of the user plane traffic to the smallcell. This offload is referred to as a data offload. When a data offloadhas been performed from the macro cell 104 to the small cell 106, then aUE that has a dual connection can transmit or receive data to and fromthe corresponding small cell wireless access network node 108.Additionally, the UE 110 can also communicate user plane traffic withthe macro eNB 104. Although reference is made to data offload to onesmall cell, it is noted that in other examples, the macro cell 104 canperform data offload for the UE 110 to multiple small cells.

Discovery of a Small Cell eNB in an Off State

When a small cell eNB is in an off state, and a UE moves into thecoverage area of the small cell eNB, it may be beneficial to activatethe small cell eNB from the off state to the on state, particularly ifthe UE has a relatively large amount of data traffic to communicate.However, since a small cell eNB has turned off its downlinktransmissions in the off state, a UE may not be able to determine thatthe UE is nearby a small cell eNB that is in an off state, and thus,would not a be able to establish a connection with the small cell eNBthat is in the off state.

A small cell eNB in an off state is also referred to as a “sleepingsmall cell eNB.”

In accordance with some implementations, the sleeping small cell eNB cancontinue to send a discovery signal even though the small cell eNB is inthe off state. The discovery signal can be an existing signal withenhancements or modifications or a new signal. A new signal refers to asignal that is not provided by current standards, but which may (or maynot) be defined by future standards. An existing signal refers to asignal provided by current standards.

FIG. 2 is a flow diagram of a process of a small cell eNB according tosome implementations. The small cell eNB receives (at 202) informationrelating to a configuration for the discovery signal. Once the smallcell eNB enters into an off state, the small cell eNB would deactivatedownlink transmissions that the small cell eNB would normally send whenthe small cell eNB is in the on state. However, in the off state, thesmall cell eNB can transmit (at 204) the discovery signal according tothe configuration, where the transmitted discovery signal is fordetection by a UE to allow the UE to detect that the UE is nearby thesmall cell eNB that is in the off state (e.g. within the coverage areaof the small cell eNB). Thus, once a UE enters the coverage area of asleeping small cell eNB, even though the UE is not served by this smallcell eNB, the UE can still detect the discovery signal transmitted bythe sleeping small cell eNB.

The configuration received at 202 can specify at least onecharacteristic of the discovery signal. For example, the characteristiccan include the subframes and the time and frequency resource withineach of the subframes used for transmitting the discovery signal. Thetransmission may occur periodically. In this case, a timing of thediscovery signal, such as the periodicity of the discovery signal, or anoffset at which the discovery signal is located. The periodicity of thediscovery signal specifies a time interval between periodictransmissions of the discovery signal. The offset can indicate thestarting point of the discovery signal. In implementations where dataand control information are carried in frames (also referred to as radioframes or system frames), a subframe can be identified by a system frameindex and a subframe index with the system frame. For example, asubframe can be identified as (n_(f),i), where n_(f) is the system frameindex and i is the subframe index within the system frame. Let N_(sf) bethe number of subframes in a system frame, then for a discovery signalconfigured with periodicity M_(p) and subframe offset M_(offset), thediscovery signal would be transmitted on subframes (n_(f),i) satisfying(N_(sf)·n_(f)+i−M_(offset))mod(M_(P))=0, where mod is a modulo function.

A sleeping small cell eNB can still periodically transmit a discoverysignal according to a specified periodicity (as specified by theconfiguration). FIG. 3 illustrates example downlink transmissions of asmall cell eNB. First transmissions (302) are by the small cell eNB whenthe small cell is active (in the on state). Second transmissions (304)are by the small cell eNB in the off state.

The transmissions 302 and 304 are made in system frames (frame #0, frame#1, and frame #2 depicted in FIG. 3). Each system frame includes anumber (e.g. 10) of subframes (each subframe is represented as a box inFIG. 3). A subframe has a specified time duration over which data orcontrol information, or both, can be carried. Each box filled with ahash pattern represents a subframe that carries at least onesynchronization signal. More specifically, in some examples, the hashedboxes represent subframes that carry a primary synchronization signal(PSS) and a secondary synchronization signal (SSS), as defined by the3GPP standards.

In the first transmissions (302) by the active small cell eNB, thesynchronization signals are transmitted at a first periodicity. However,in the second transmissions (304) by the small cell eNB in the offstate, the synchronization signals are transmitted at a second, largerperiodicity. A larger periodicity refers to a longer period (or longertime duration between transmissions of the synchronization signals).

In the FIG. 3 example, it is assumed that the PSS or SSS, or both, is(or are) used as a discovery signal transmitted by the small cell eNB inthe off state. In the second transmissions (304), the configuration(received at 202 in FIG. 2) can specify the periodicity (306) oftransmission of the discovery signal, as well as the frame offset (308)that indicates the starting point of the discovery signal. In thedepicted example, a PSS or SSS is an example of an existing signal thatcan be used as a discovery signal.

Note that when used as a discovery signal transmitted by a sleepingsmall cell eNB, the PSS or SSS is transmitted at a larger periodicitythan the periodicity of the PSS or SSS sent by an active eNB. In theexample of FIG. 3, the active small cell eNB transmits a PSS/SSS everyfive subframes, while the sleeping small cell eNB transmits a PSS/SSSevery 20 subframes.

Another example of an existing signal that can be used as a discoverysignal that can be transmitted by a sleeping small cell eNB is acell-specific reference signal (CRS). Normally, a CRS transmitted by aneNB can be used for estimating a condition of a downlink channel. A CRSused as a discovery signal can be transmitted by a sleeping small celleNB with a larger periodicity than a CRS transmitted by an active smallcell eNB.

It is noted that the remaining subframes (those represented by the blankboxes in FIG. 3) in the second transmissions (304) are kept silent—inother words, these subframes do not include any signals. (Note thatdepending upon a subframe configuration, some of the subframes may havebeen assigned to carry uplink information from a UE to the small celleNB in a time division duplex (TDD) system).

In some implementations, the UE can report information pertaining to thedetected discovery signal to another network node (referred to as a“coordinating network node”), such as the macro eNB 104 (FIG. 1), oranother (active) small cell eNB, or a network node in the core network118 (FIG. 1). The reported information can include any one or more ofthe following: an identifier of the received discovery signal, a cellidentifier (to identify a cell), a received signal strength of the smallcell eNB that is in the off state, and other cell-specific information.

The coordinating network node can collect the reported information fromthe UE, as well as from other UEs that have detected the discoverysignals of the sleeping small cell eNB. The coordinating network nodecan decide, based on the reported information from the UEs, whether thesleeping small cell eNB should be turned on to serve the UE. If so, thecoordinating network node can signal the decision to the sleeping smallcell eNB, and possibly to the UE. A command to awaken a sleeping smallcell eNB can be sent on a backhaul link (e.g. 116 in FIG. 1), over theair, or over a link between the core network 118 and the sleeping smallcell eNB.

In some examples, a command can also be sent to the UE to perform signalstrength measurements for the small cell eNB that has been activatedfrom the off state to the on state. Alternatively, the UE does not haveto be notified that the formerly sleeping small cell eNB has beenactivated; rather, the UE can autonomously check to determine if thesleeping small cell eNB has awakened to the on state. Once the smallcell eNB is turned on, the UE can measure the signal strength of thenewly activated small cell eNB. If the signal strength of this newlyactivated small cell eNB is stronger than the detected signal strengthof the small cell eNB that currently serves the UE (or some otherhandover criterion is satisfied), then a handover operation can betriggered to hand over the UE from the serving small cell eNB to thenewly activated small cell eNB.

To facilitate the transmission of discovery signals, the sleeping smallcell eNB can maintain synchronization with one or more other networknodes, such as the macro eNB 102 and other small cell eNBs.Synchronization can be maintained between eNBs over backhaul links orover an air interface

In some examples, the coordinating network node, such as the macro eNB104 or another node, can provide assistance to help a sleeping smallcell eNB in setting an effective periodicity of transmissions of adiscovery signal. For example, the coordinating network node candynamically modify the periodicity, such as based on a traffic loadobserved by the coordinating network node. If there is a higher trafficload detected by the coordinating network node, the coordinating networknode can notify a sleeping small cell eNB (or multiple small cell eNBs)to transmit a discovery signal at a smaller periodicity (i.e. morefrequently). More frequent transmissions of the discovery signal by asleeping small cell eNB increases the possibility of the sleeping smallcell eNB being detected by UEs.

To facilitate detection of a discovery signal transmitted by a sleepingsmall cell eNB, a macro eNB or another active eNB can send, to a UE,configuration information pertaining to the discovery signal. Theconfiguration information can include at least one of timinginformation, such as the periodicity and/or time offset (e.g. systemframe number), a time and/or frequency resource within a subframe, asignal waveform information of the discovery signal, or otherinformation. The configuration information can also identify anothercharacteristic of the discovery signal.

The signal waveform information can refer to a cell-specific signaltransmitted by the sleeping small cell eNB. The cell-specific signal canbe a CRS transmitted by the sleeping small cell eNB, or cell-specificsynchronization signal (e.g. PSS or SSS) transmitted by the sleepingsmall cell eNB.

The configuration relating to the time and/or frequency resource canspecify a subset of a time and/or frequency resource configured for aCRS transmitted by a small cell eNB. Alternatively, the time and/orfrequency resource can be different from a time and/or frequencyresource configured for a CRS transmitted by the small cell eNB.

The configuration information can be signaled to the UE using higherlayer messaging, such as a Radio Resource Control (RRC) message, whichcan include a dedicated RRC message (that is sent to a particular UE) ora broadcast RRC message (that is broadcast to multiple UEs).

In implementations where synchronization is maintained between thesleeping small cell eNB and other network nodes, a UE can use theconfiguration information to obtain the approximate timing of thesubframes in which the discovery signal from a sleeping small cell eNBis transmitted. The UE can perform detection of the discovery signal inthose subframes.

An example of a modified version of an existing RRC message is providedbelow. More specifically, the following depicts a modified version of aRadioResourceConfigDedicated information element as described in 3GPP TS36.331. In the example below, the underlined text indicates newinformation elements that are currently not specified in the 3GPPstandards. A new information element refers to an information elementthat is not provided by current standards, but which may (or may not) bedefined by future standards. An existing information element refers toan information element provided by current standards.

-- ASN1START RadioResourceConfigDedicated ::= SEQUENCE {srb-ToAddModList SRB-ToAddModList OPTIONAL, -- Cond HO-Conndrb-ToAddModList DRB-ToAddModList OPTIONAL, -- Cond HO-toEUTRAdrb-ToReleaseList DRB-ToReleaseList OPTIONAL, -- Need ON mac-MainConfigCHOICE { explicitValue MAC-MainConfig, defaultValue NULL } OPTIONAL, --Cond HO-toEUTRA2 sps-Config SPS-Config OPTIONAL, -- Need ONphysicalConfigDedicated PhysicalConfigDedicated OPTIONAL, -- Need ON..., [[ rlf-TimersAndConstants-r9 RLF-TimersAndConstants-r9 OPTIONAL --Need ON ]], [[ measSubframePatternPCell-r10 MeasSubframePatternPCell-r10OPTIONAL -- Need ON ]], [[ neighCellsCRS-Info-r11 NeighCellsCRS-Info-r11OPTIONAL -- Need ON ]] [[ NeighSmallCellsDS-Info-r12NeighSmallCellsDS-Info-r12  OPTIONAL -- Need ON ]] }RadioResourceConfigDedicatedSCell-r10 ::= SEQUENCE { -- UE specificconfiguration extensions applicable for an SCellphysicalConfigDedicatedSCell-r10 PhysicalConfigDedicatedSCell-r10OPTIONAL, -- Need ON ..., [[ mac-MainConfigSCell-r11MAC-MainConfigSCell-r11 OPTIONAL -- Cond SCellAdd ]] } SRB-ToAddModList::= SEQUENCE (SIZE (1..2)) OF SRB-ToAddMod SRB-ToAddMod ::= SEQUENCE {srb-Identity INTEGER (1..2), rlc-Config CHOICE { explicitValueRLC-Config, defaultValue NULL } OPTIONAL, -- Cond SetuplogicalChannelConfig CHOICE { explicitValue LogicalChannelConfig,defaultValue NULL } OPTIONAL, -- Cond Setup ... } DRB-ToAddModList ::=SEQUENCE (SIZE ( 1..maxDRB)) OF DRB-ToAddMod DRB-ToAddMod ::= SEQUENCE {eps-BearerIdentity INTEGER (0..15) OPTIONAL, -- Cond DRB-Setupdrb-Identity DRB-Identity, pdcp-Config PDCP-Config OPTIONAL, -- CondPDCP rlc-Config RLC-Config OPTIONAL, -- Cond SetuplogicalChannelIdentity INTEGER (3..10) OPTIONAL, -- Cond DRB-SetuplogicalChannelConfig LogicalChannelConfig OPTIONAL, -- Cond Setup ... }DRB-ToReleaseList ::= SEQUENCE (SIZE (1..maxDRB)) OF DRB-IdentityMeasSubframePatternPCell-r10 ::= CHOICE { release NULL, setupMeasSubframePattern-r10 } NeighCellsCRS-Info-r11 ::= CHOICE { releaseNULL, setup CRS-AssistanceInfoList-r11 } CRS-AssistanceInfoList-r11 ::=SEQUENCE (SIZE (1..maxCellReport)) OF CRS-AssistanceInfo-r11CRS-AssistanceInfo-r11 ::= SEQUENCE { physCellId-r11 PhysCellId,antennaPortsCount-r11 ENUMERATED {an1, an2 , an4 , spare1},mbsfn-SubframeConfigList-r11 MBSFN-SubframeConfigList, ... }NeighSmallCellsDS-Info-r12 ::= CHOICE { release  NULL, setup DS-ConfigurationInfo-r12 } DS-ConfigurationInfo-r12 ::= SEQUENCE {DS-TransmissionInterval-r12 ENUMERATED{  sf20, sf40, sf80, sf160, sf320 sf640}, DS-offset-r12 ENUMERATED{  10, 20, 40, 60, 80, 160, 320, 480,640}, ... } -- ASN1STOP

In the foregoing example, the DS-TransmissionInterval informationelement specifies a periodicity of the discovery signal, referred to asNeighSmallCellsDS-Info. Also, the DS-offset information elementspecifies the time offset of the discovery signal.

The foregoing describes implementations in which existing signals areused as discovery signals. In alternative implementations, new discoverysignals can be used instead of existing signals.

A new discovery signal can have a relatively longer transmissionperiodicity, to avoid transmitting the discovery signal too frequently.In some examples, the new discovery signal can be derived from aspecified sequence (also referred to as a “discovery sequence”). Forexample, different small cell eNBs can transmit discovery signals withdifferent discovery sequences. The discovery sequences that aretransmitted by neighboring small cell eNBs can be orthogonal sequencesor quasi-orthogonal sequences.

In some examples, a sequence used for a discovery signal can bedependent upon a cell identifier that identifies the cell of therespective small cell eNB. In a more specific example, the cellidentifier can be used as an initial seed in generating the discoverysequence. In this way, different discovery sequences can be mapped todifferent cell identifiers.

A UE can be notified of a pool of discovery sequences and theirrelations to cell identifiers in higher layer messaging, such as RRCmessaging. In this way, based on a detected discovery sequence, the UEcan determine the respective cell identifier associated with thesleeping small cell eNB that transmitted the discovery sequence detectedby the UE.

In some implementations, a discovery sequence can have a longer lengththan a sequence used for a synchronization signal, such as PSS or SSS.

In further implementations, the duplex mode of a small cell eNB can beindicated by a discovery sequence or by a resource for carrying adiscovery signal, or both. For example, a first pool of discoverysequences can be used for small cell eNBs that operate according to afrequency division duplex (FDD) mode, and a second pool of discoverysequences can be used for small cell eNBs that operate according to atime division duplex (TDD) mode. In FDD mode, uplink and downlinktransmissions are separated in the frequency domain, by transmittinguplink data using a first carrier frequency, and transmitting downlinkdata using a second carrier frequency. In TDD mode, both uplink anddownlink transmissions occur on the same carrier frequency; however,uplink and downlink transmissions are separated in the time domain, bysending uplink and downlink transmissions in different time periods. Ifa UE detects a discovery sequence from the first pool, then the UE candetermine that the small cell eNB that transmitted the discoverysequence operates in FDD mode. Similarly, if a UE detects a discoverysequence from the second pool, then the UE can determine that the smallcell eNB that transmitted the discovery sequence operates in TDD mode.

In alternative implementations, the discovery signal transmissions canbe carried in multiple symbols (e.g. orthogonal frequency-divisionmultiplexing or OFDM symbols). A gap between symbols carrying discoverysignal transmissions can be used to indicate a duplex mode; e.g. a firstgap between symbols indicates FDD mode, while a second, different gapbetween symbols indicates TDD mode.

Discovery signals can be transmitted in one or more symbols within agiven subframe. In other examples, discovery signal transmissions canspan more than one subframe. The subframes carrying discovery signalscan be continuous or discontinuous in the time domain.

FIG. 4 depicts an example in which the second subframe (402A, 402B) ofeach system frame is used to carry a primary discovery signal, while thethird subframe (404A, 404B) of each system frame is used to carry asecondary discovery signal.

The use of primary and secondary discovery signals as depicted in FIG. 4is analogous to use of PSS and SSS (for synchronization purposes when asmall cell eNB is in an on state). A UE can first attempt to detect aprimary discovery signal transmitted by a sleeping small cell eNB.Certain information relating to the corresponding cell can be derivedfrom the primary discovery signal. Once the primary discovery signal isdetected, the UE can attempt to detect a secondary discovery signal thatis transmitted by the sleeping small cell eNB. The UE can derive furtherinformation about the corresponding cell from the secondary discoverysignal.

Various different options can be implemented for configurations used fordiscovery signals.

In Option 1, the configuration of the discovery signal can be the samefor all small cell eNBs. For example, the discovery signals transmittedby the different eNBs can have the same periodicity, time resource, andfrequency resource. A time resource can refer to a subframe (within asystem frame) and/or OFDM symbol(s) within a subframe that is (are) usedto carry a discovery signal. A frequency resource can refer to thesub-carriers or Resource Blocks (RBs) used to carry a discovery signal.

FIG. 5 depicts an example that has three small cells. As shown in FIG.5, the discovery signals 502, 504, and 506 transmitted in each of thethree small cells are carried in the same subframe (e.g. the secondsubframe of a system frame in the FIG. 5 example). Also, the discoverysignals transmitted in the three small cells have the same periodicity,and are carried on the same frequency resource (frequency is representedalong the vertical axis in FIG. 5).

According to Option 1, as depicted in FIG. 5, sleeping small cell eNBstransmit respective discovery signals simultaneously on the same timeand frequency resources. To allow for successful detection of thediscovery signals transmitted by different small cell eNBs, thediscovery sequences used for the discovery signals are orthogonal toeach other. A UE can distinguish the cell identifier of a small cellbased on the detected discovery sequence.

Alternatively, in Option 2, as shown in FIG. 6, the periodicity and timeresource (subframe) for carrying discovery signals can be the same forall small cells. However, the frequency resource used to carry discoverysignals can be different across different small cells, so that a UE candistinguish discovery signals of different small cells based on thedetected discovery sequences or the frequency resource used, or both.FIG. 6 shows that the discovery sequence 602, discovery sequence 604,and discovery sequence 606 for the three small cells are carried ondifferent frequency resources (e.g. different sub-carriers or RBs ofdifferent frequencies). The different frequency resources are indicatedby different relative positions of the sequences 602, 604, and 606 alongthe vertical axis within each corresponding subframe.

As another alternative, in Option 3, as shown in FIG. 7, the periodicityand frequency resource to carry discovery signals 702, 704, and 706 canbe the same across multiple small cells. However, the time resource usedto carry discovery signals can be different for different small cells.For example, as shown in FIG. 7, the discovery sequence for small cell 1is in the second subframe of a system frame, the discovery sequence forsmall cell 2 is in the third subframe of a system frame, and thediscovery sequence for small cell 3 is in the fourth subframe of asystem frame. With Option 3, a UE can distinguish discovery signals fromdifferent small cells based on the detected discovery sequences or thetime resource used, or both.

Note that a time resource for carrying a discovery signal can include asubframe, or an OFDM symbol, or both. For example, discovery signals ofdifferent small cells can be distinguished by different OFDM symbolsthat are used to carry the discovery signals, or by different subframeindices of subframes used to carry the discovery signals.

In further alternative implementations, in Option 4, the configurationsof discovery signals for different small cells can be based onrespective unique combinations of periodicity, frequency, sequence, andtime. For example, the configuration of a discovery signal for a firstsmall cell can be based on a first combination of periodicity,frequency, sequence, and time, while the configuration of a discoverysignal for a second small cell can be based on a second, differentcombination of periodicity, frequency, sequence, and time,

The configuration for a discovery signal of a given small cell can besent to a UE by the macro eNB 104 or another active small cell eNB.After receiving the configuration, the UE can perform detection of asleeping small cell eNB based on detection of the discovery signalaccording to the configuration.

In some examples, the configuration containing the periodicity, timeresource, frequency resource, and sequence can be included in adedicated RRC message sent to the UE. In other examples, theconfiguration can be sent to the UE in a broadcast RRC message, such asin a System Information Block (SIB). For example, the configuration forthe discovery signal can be carried in a new information element of SIBtype 4 or 5, or in a new SIB.

An example of a modified RadioResourceConfigDedicated informationelement that can be carried in an RRC message is provided below(underlined text indicates new information elements):

-- ASN1START RadioResourceConfigDedicated ::= SEQUENCE {srb-ToAddModList SRB-ToAddModList OPTIONAL, -- Cond HO-Conndrb-ToAddModList DRB-ToAddModList OPTIONAL, -- Cond HO- toEUTRAdrb-ToReleaseList DRB-ToReleaseList OPTIONAL, -- Need ON mac-MainConfigCHOICE { explicitValue MAC-MainConfig, defaultValue NULL } OPTIONAL, --Cond HO- toEUTRA2 sps-Config SPS-Config OPTIONAL, -- Need ONphysicalConfigDedicated PhysicalConfigDedicated OPTIONAL, -- Need ON..., [[ rlf-TimersAndConstants-r9 RLF-TimersAndConstants-r9 OPTIONAL --Need ON ]], [[ measSubframePatternPCell-r10 MeasSubframePatternPCell-r10OPTIONAL -- Need ON ]], [[ neighCellsCRS-Info-r11 NeighCellsCRS-Info-r11OPTIONAL -- Need ON ]] [[ NeighSmallCellsDS-Info-r12NeighSmallCellsDS-Info-r12 OPTIONAL -- Need ON ]] }RadioResourceConfigDedicatedSCell-r10 ::= SEQUENCE { -- UE specificconfiguration extensions applicable for an SCellphysicalConfigDedicatedSCell-r10 PhysicalConfigDedicatedSCell-r10OPTIONAL, -- Need ON ..., [[ mac-MainConfigSCell-r11MAC-MainConfigSCell-r11 OPTIONAL -- Cond SCellAdd ]] } SRB-ToAddModList::= SEQUENCE (SIZE (1..2)) OF SRB-ToAddMod SRB-ToAddMod ::= SEQUENCE {srb-Identity INTEGER (1..2), rlc-Config CHOICE { explicitValueRLC-Config, defaultValue NULL } OPTIONAL, -- Cond SetuplogicalChannelConfig CHOICE { explicitValue LogicalChannelConfig,defaultValue NULL } OPTIONAL, -- Cond Setup ... } DRB-ToAddModList ::=SEQUENCE (SIZE (1..maxDRB)) OF DRB-ToAddMod DRB-ToAddMod ::= SEQUENCE {eps-BearerIdentity INTEGER (0..15) OPTIONAL, -- Cond DRB-Setupdrb-Identity DRB-Identity, pdcp-Config PDCP-Config OPTIONAL, -- CondPDCP rlc-Config RLC-Config OPTIONAL, -- Cond SetuplogicalChannelIdentity INTEGER (3..10) OPTIONAL, -- Cond DRB-SetuplogicalChannelConfig LogicalChannelConfig OPTIONAL, -- Cond Setup ... }DRB-ToReleaseList ::= SEQUENCE (SIZE (1..maxDRB)) OF DRB-IdentityMeasSubframePatternPCell-r10 ::= CHOICE { release NULL, setupMeasSubframePattern-r10 } NeighCellsCRS-Info-r11 ::= CHOICE { releaseNULL, setup CRS-AssistanceInfoList-r11 } CRS-AssistanceInfoList-r11 ::=SEQUENCE (SIZE (1..maxCellReport)) OF CRS-AssistanceInfo-r11CRS-AssistanceInfo-r11 ::= SEQUENCE { physCellId-r11 PhysCellId,antennaPortsCount-r11 ENUMERATED {an1, an2 , an4 , spare1},mbsfn-SubframeConfigList-r11 MBSFN-SubframeConfigList, ... }NeighSmallCellsDS-Info-r12 ::= CHOICE { release  NULL, setup DS-ConfigurationInfo-r12 } DS-ConfigurationInfo-r12 ::= SEQUENCE {DS-TransmissionInterval-r12 ENUMERATED{  sf20, sf40, sf80, sf160, sf320 sf640}, DS-SubframePattern-r12  BIT STRING (SIZE (40)),DS-FrequencyPattern-r12  BIT STRING (SIZE (dl-bandwidth)),DS-offset-r12  ENUMERATED{  10, 20, 40, 60, 80, 160, 320, 480, 640}, ...} -- ASN1STOP

In the foregoing example, a DS-TransmissionInterval information elementspecifies the periodicity, a DS-SubframePattern information elementspecifies a subframe of a system frame in which the discovery signal iscarried, a DS-FrequencyPattern information element specifies a carrieror frequency on which the discovery signal is carried, and a DS-Offsetinformation element specifies the time offset (e.g. system frame number)of the discovery signal.

In some implementations, the macro eNB 104 or an active serving smallcell eNB can send a mapping table (or other mapping data structure) to aUE. The mapping table maps cell identifiers with respectiveconfigurations of discovery signals. The mapping table can also beincluded in a dedicated or broadcast RRC message.

The configuration contained in the mapping table can include one or acombination of the following: the sequence of each discovery signal, andcharacteristic information (e.g. periodicity, time, and frequency) ofthe resource used to carry each discovery signal. When a UE detects atransmitted discovery signals, the UE can derive the cell identifier,using the mapping table, of the sleeping small cell eNB that transmittedthe discovery signal. The UE can also determine the signal strength ofthe detected discovery signal. The UE can report feedback information(including the cell identifier and signal strength, for example)relating to the detected sleeping small cell eNB to the macro eNB 104,or to another active serving small cell eNB.

In response, a coordinating network node, such as the macro eNB 104, anactive serving small cell eNB, or another network node, can send acommand to awaken the sleeping small cell eNB to the on state, where thecommand can be sent on a backhaul link (e.g. 116 in FIG. 1), over theair, or over a link between the core network 118 and the sleeping smallcell eNB.

To reduce the complexity of the sequence design associated with sendingconfiguration information, the discovery sequences can be the same assequences as synchronization signals (e.g. PSS/SSS) that are alreadysent by an active small cell eNB. However, the discovery sequences canhave longer periods than the PSS/SSS sequences. A UE can distinguish adiscovery sequence from a PSS/SSS sequence based on the periodicity ofthe detected sequence. In this manner, configuration informationrelating to the time and frequency resources of the discovery sequencesthat are the same as the configuration information of the PSS/SSSsequences would not have to be re-sent.

Alternatively, the macro eNB 104 or an active small cell eNB can send alist of sleeping small cell eNBs (but not with explicit discovery signalconfiguration), and the UE can determine the corresponding discoverysignals based on the detected periodicity.

A coordinating network node, such as the macro eNB 104, an active smallcell eNB, or another network node, can provide assistance information toset the periodicity of discovery signals, which can be based on adetected traffic load.

If the macro and small cell eNBs operate on different carriers, it canbe assumed that no interference exists between the macro and small celleNBs. However, if the macro and small cell eNBs operate on the samecarrier, there may be interference between downlink transmissions of themacro eNB 104 and the downlink transmissions of discovery signals of thesmall cell eNBs. This may degrade the ability of a UE to detect adiscovery signal transmitted by a sleeping small cell eNB.

To address the interference issue, examples of some solutions aredescribed below.

In some examples, a UE can perform UE-side interference control, basedon the UE's knowledge of the time and frequency resources used by smallcell eNBs for transmitting discovery signals.

In alternative examples, the macro eNB 104 can mute downlinktransmissions on the time and frequency resources that small cell eNBsuse to transmit discovery signals.

Discovering a UE by a Sleeping Small Cell eNB

The foregoing describes implementations to allow a UE to detect sleepingsmall cell eNBs. The following describes implementations to allow asleeping small cell eNB to detect a nearby UE (e.g. a UE that hasentered a coverage area of the sleeping small cell eNB).

In some examples, a sleeping small cell eNB does not transmit anydownlink signals including the discovery signals as discussed above. Thesleeping small cell eNB can continue to monitor an uplink transmissionfrom a UE. In response to detecting a nearby UE based on the detectionof the UE's uplink transmission, the sleeping small cell eNB can performa procedure to cause the sleeping small cell eNB to be awakened.

FIG. 8 illustrates an example process of detecting a nearby UE. Thesmall cell eNB receives (at 802) information relating to a configurationof an uplink transmission of a UE to enable the wireless access networknode to detect the uplink transmission. Once the small cell eNB hasentered an off state, the sleeping small cell NB can monitor (at 804)for the uplink transmission of the UE according to the configuration.

In some implementations, the uplink transmission of a UE to be detectedby a sleeping small cell eNB can be an existing uplink signal. In suchimplementations, the macro eNB 104 or other coordinating network nodecan transfer configuration information to a small cell eNB to enable thedetection of a UE. The existing uplink signal can include a signaltransmitted in a Physical Random Access Channel (PRACH). The PRACHsignal is normally used by the UE to perform a random access procedureto establish a connection with an eNB (e.g. macro eNB 104 or a smallcell eNB). Alternatively, the existing uplink signal that can bemonitored by a sleeping small cell eNB can be a sounding referencesignal (SRS), which is normally monitored by an eNB for determining anuplink channel quality. In other examples, other existing uplink signalscan be monitored by a sleeping small cell eNB.

In examples where a sleeping small cell eNB is to monitor for an SRS ofa UE, the macro eNB 104 or other coordinating network node can notifythe small cell eNB of the SRS configuration, such as over the backhaullink. Using the SRS configuration, the sleeping small cell eNB canmonitor for the SRS transmission to determine if there is a nearby UE.In such examples, synchronization may have to be maintained between themacro eNB 104 and the sleeping small cell eNB.

In other examples where a sleeping small cell eNB is to monitor for aPRACH transmission from a UE, the macro eNB 104 can send configurationinformation pertaining to the PRACH to the small cell eNB. Suchconfiguration information can include the PRACH preamble andconfiguration (e.g. subframe number and frequency resource) for thePRACH.

A sleeping small cell eNB can then use the PRACH configuration tomonitor for a PRACH. It may be difficult for a sleeping small cell eNBto determine which UE transmitted a PRACH, since a UE may randomlyselect a PRACH to transmit. However, the sleeping small cell eNB may nothave to be aware of the identity of the nearby UE. The sleeping smallcell eNB may simply make a determination that any UE is nearby.

Thus, when a PRACH is detected, the sleeping small cell eNB can send thedetected PRACH, which is identified by a preamble number, subframenumber, and frequency resource where the preamble was detected, and theassociated receive power (or the power difference between the receivedand the target power in the small cell), to a coordinating network node,such as the macro eNB 104, an active small cell eNB, or another networknode. The macro eNB 104 may compare the received power for the PRACHfrom multiple sleeping small cell eNBs as well as the preamble powerlevel detected by the macro eNB 104 (or a threshold), and can determinewhether the UE is nearby to one of the multiple sleeping small celleNBs. The threshold may be the PRACH initial target received powerconfigured in the macro cell plus some margin, which can be proportionalto the ratio of output power of the macro and the small cell eNBs.

An example is shown in FIG. 9, where the UE 110 that is nearby smallcell #1 transmits PRACH (902) to the macro eNB 104 using the PRACHconfiguration of the macro cell 102. The PRACH configuration is signaledby the macro eNB 104 to the two small cell eNBs 108 over backhaul links116. The PRACH configuration can specify subframes (904, 906) and thefrequency on which the PRACH (902) is to be transmitted.

The small cell eNBs 108 can monitor for PRACH in the subframes (904,906). Once detected, the small cell eNBs 108 can report informationpertaining to the detected PRACH to the macro eNB 104 over respectivebackhaul links. Because the UE is closer to small cell #1, the detectedPRACH power (908) in small cell #1 is higher than the detected PRACHpower (910) in the macro cell 102 and the detected PRACH power (912) insmall cell #2. Based on a comparison of the detected PRACH power levels(910, 912, and 914), the macro eNB 104 determines that the detectedPRACH power level 910 is highest at small cell #1. As a result, themacro eNB 104 can inform the small cell eNB 108 of small cell #1 aboutthe presence of the UE 110.

In alternative solutions, instead of monitoring for existing uplinksignals from a UE, a sleeping small cell eNB can monitor for a newuplink signal. In some examples, the new uplink signal can be derivedfrom an uplink sequence for the purpose of carrying additionalinformation. There can be multiple different uplink sequences, and eachsequence can carry different information.

In some examples, as shown in FIG. 10, different uplink sequences1000_1, 1000_2, . . . , 1000_N (where N>1) can be mapped to differentrespective power levels (1 to N). The power level information can beimplicitly indicated by the uplink sequence.

Meanwhile, the resource to carry the uplink sequence can be informed toUEs by dedicated or broadcast RRC messages. The UEs could transmit theselected uplink sequence on the informed resource.

For example, the macro eNB 104 can send a mapping table (or othermapping data structure) that maps between uplink sequences andrespective power levels, to a UE, using dedicated or broadcast RRCmessaging. Then, when the UE is configured to send this new uplinksignal, the UE can select the uplink sequence that reflects the powerlevel of uplink transmissions of the UE. A sleeping small cell eNB candetermine the power level of the UE based on the detected uplinksequence, and can then calculate the pathloss to the UE and decide ifthe sleeping small cell eNB should be activated.

More generally, the decision to determine whether to awaken the sleepingsmall cell eNB can be based on at least one of a power level of adetected uplink signal, a target received power at the sleeping smallcell eNB, a maximum transmit power configured at the sleeping small celleNB, a received power at a small cell eNB serving the UE, a maximumtransmit power configured at the small cell eNB serving the UE.

In further examples in which a UE does not currently have any servingcell and is attempting to find a serving cell to provide services, theUE can transmit a new uplink signal, which may be known to the UE evenif the UE is not currently attached to any serving cell. When a sleepingsmall cell eNB detects the uplink signal, the sleeping small cell eNBcan determine that there is a nearby UE to be served. In this case, thesmall cell eNB may not have to derive the power level from the detecteduplink signal initiate a procedure to cause activation of the sleepingsmall cell eNB in response to detecting the uplink signal to serve theUE.

In further examples, the macro eNB 104 can assist the sleeping smallcell eNB in locating a UE. For example, if the small cell eNB's locationinformation is known by the macro eNB 104 in advance, and the macro eNB104 can obtain an estimated location of a the UE (such as based onfeedback information or based on a positioning technique such as anobserved time difference of arrival or OTDOA technique), then the macroeNB 104 can determine if a UE is nearby the small cell eNB.Alternatively, the macro eNB 104 can estimate the downlink pathloss tothe UE based on the macro eNB's transmit power and feedback information(e.g. a measured Reference Signal Received Power or RSRP) from the UE.The downlink pathloss can be used by the macro eNB 104 to infer anuplink pathloss from the UE, in scenarios where the uplink and downlinkchannels are reciprocal, such as when TDD is used. From the downlinkpathloss, the macro eNB 104 can estimate the location of the UE. Oncethe location of the UE is estimated, the macro eNB 104 can inform thesleeping small cell eNB of the UE's location.

In yet another alternative example, as the UE can be served by anotheractive small cell eNB, the other active small cell eNB can adjusts theUE's uplink transmit power so that the arrival power at the active smallcell eNB is approximately at a target power level. The sleeping smallcell eNB can check the received power from the UE and determine if thereceived power is above or lower than the target power level. If thereceived power is above the target power level, that means the UE iscloser to the sleeping small cell eNB.

In general, multiple sleeping small cell eNBs can measure the uplinktransmit power from a UE, and the network (either a macro eNB or a headof a small cell cluster) can collect such measured power and compare themeasured uplink transmit powers. The small cell eNB that with thelargest received power can be considered as the one that is closest tothe UE.

Transitioning a Small Cell eNB Between an On State and an Off State

The following describes implementations that can be employed totransition a small cell eNB from an on state to an off state withreduced impact on UEs within a coverage of the small cell eNB. Note thatturning off a small cell eNB abruptly can cause interruption of datacommunications of UEs served by the small cell eNB, or of thecommunication of paging messages to UEs camped on the small cell eNB.

In accordance with some implementations, instead of turning off a givensmall cell eNB abruptly, the given small cell eNB can be graduallyturned off. For example, the transmit power of the given small cell eNBcan be gradually decreased to gradually shrink the coverage area of thegiven small cell eNB. This would allow UEs currently camped on the givensmall cell eNB to select other small cells. Also, reducing the transmitpower would discourage UEs from camping on the given small cell eNB. Thegiven small cell eNB can be turned off once the minimum transmit poweris reached.

As discussed below, one or more timers can be used to control thegradual turnoff of a small cell eNB.

In the following, a small cell eNB can have several different offstates, including a semi-off state (in which the transmit power of thesmall cell eNB is reduced), an off state (in which the small cell eNBcan transmit minimal signaling, such as discovery signals, but does nottransmit other signals), and a deep-off state (in which the small celleNB does not transmit any signals and also not monitor the UE uplinktransmission).

As shown in FIG. 11, a first timer 1102 in the small cell eNB can beused for moving the small cell eNB from an on state to a semi-off state.The first timer 1102 is started when the small cell eNB determines thatit does not have to serve any UEs anymore. This can occur as a result of(1) a mobility procedure in which the last UE previously served by thesmall cell eNB has been handed over to another cell; or (2) the last UEhas moved from a connected state to an idle state.

Once the first timer 1102 expires, the small cell eNB can transitionfrom the on state to the semi-off state. While in the semi-off state,the small cell eNB can gradually reduce its transmit power to shrink itscoverage area. For example, the small cell eNB can transmit thefollowing signals with reduced power: PSS, SSS, Physical BroadcastChannel (PBCH), CRS, SIB type 1, SIB type 2, and so forth. A UE closerto a small cell eNB is able to detect and perform a random accessprocedure (on PRACH) with the small cell eNB in the semi-off state.

Alternatively the small cell eNB can adjust parameters in the SIBs todiscourage UEs from camping on it. In an example, the small cell eNB canincrease one or both of a q-QualMin parameter and a q-RxLevMin parameter(as defined by 3GPP standards) for cell selection. In another example,the small cell eNB can increase one or both of an s-IntraSearchPparameter and an s-IntraSearchQ parameter (as defined by 3GPP standards)for cell reselection. In another example, the small cell eNB can selecta lower value for a q-Hyst (as defined by 3GPP standards) parameter forintra-frequency cell (re)selection.

While in the semi-off state, the small cell eNB can continue to sendpaging messages to UEs served by the small cell eNB. Since the smallcell is at a reduced activity level in the semi-off state, the smallcell eNB can modify paging-related parameters in SIB type 2 to reducethe number of occasions that the small cell eNB schedules potentialpaging messages. For example, the small cell eNB can assign adefaultPagingCycle T to 256 radio frames (i.e. highest value asspecified by current 3GPP standards), and a parameter nB to 1/32T (i.e.lowest value as specified by current 3GPP standards).

Since the transmit power level is reduced in the semi-off state, therange reachable by a paging signal is reduced, thus reducing the numberof UEs that are capable of receiving paging messages from the semi-offsmall cell eNB.

A second timer 1104 can be used to move the small cell eNB from asemi-off state to an off-state. The second timer 1104 is started inresponse to the small cell eNB transitioning to the semi-off state.

The second timer 1104 can be reset if the small cell eNB detects a newUE that is to be connected to the small cell eNB (in the semi-offstate). This may be due to downlink data arrival from the macro eNB 104or a core network node, or due to receipt of an uplink PRACH from a UE.The small cell eNB may even choose to transition out of the semi-offstate back to the on state, in response to reset of the second timer1104. When transitioning back to the on state, various operationparameters (such as the transmit power level, cell (re)selectionparameters, paging parameters, etc.) that are provided in SIBs can berestored to normal operation levels.

In response to expiration of the second timer 1104, the small cell eNBcan transition from the semi-off state to the off state. While in offstate, the small cell eNB only transmits discovery signals, as discussedabove. While a UE is able to detect the presence of a small cell eNB inan off state, the UE is not able to immediately perform a random accessprocedure with the small cell eNB in the off state.

In the off state, the small cell can transmit discovery signals usingthe normal transmission power such that the coverage area is notreduced.

In some examples, a third timer 1106 can be used to move the small celleNB from a semi-off state or off state to a deep-off state. Depending onnetwork setup, the third timer 1106 can be started in response to thesmall cell eNB transitioning to the semi-off state or off state. Notethat the third timer 1106 can be used in place of or in addition to thesecond timer 1104.

The third timer 1106 can be reset if there is a new UE that is to beconnected to the small cell eNB. This may be due to downlink dataarrival from the macro eNB 104 or a core network node or uplink PRACHreceived at the small cell eNB. The small cell eNB may choose totransition to the on state in response to reset of the third timer 1106.

When the third timer 1106 expires, the small cell eNB can transition tothe deep-off state. While in the deep-off state, the small cell eNB doesnot even transmit discovery signals and also not monitor the UE uplinktransmission. However, the deep-off small cell eNB can still communicateover a backhaul link with another eNB.

In alternative examples, it is possible to start the third timer 1106when the small cell eNB determines that it does not have to serve anyUEs anymore. This can be due to (a) a mobility procedure where the lastUE is handed over to another cell; or (b) the last UE having moved fromthe connected state to the idle state. In this case, upon expiration ofthe third timer 1106, the small cell eNB may move directly from the onstate to the deep-off state. In such alternative examples, the thirdtimer 1106 is used in place of the first and second timers 1102 and 1104(in other words, the timers 1102 and 1104 may be omitted).

In general, according to some implementations, a wireless access networknode includes a first timer that is started in response to an event.Upon expiration of the first timer, the wireless access network nodetransitions from a first power state to a second power state. In thesecond power state, the wireless access network node may graduallyshrink its coverage area for instance by reducing the wireless accessnetwork node's transmit power.

The wireless access network node further includes a second timer that isstarted in response to the wireless access network node transitioning tothe second power state. Upon expiration of the second timer, thewireless access network node transitions from the second power state toa third power state.

In the third power state, the wireless access network node transmits adiscovery signal but does not transmit data and other control signals.

The wireless access network node further includes a third timer that isstarted in response to an event which can be the wireless access networknode transitioning to the second or third power states. Upon expirationof the third timer, the wireless access network node transitions to afourth power state. In the fourth power state, the wireless accessnetwork node does not transmit any signals.

Awaking a Small Cell eNB from an Off State

When a small cell eNB is in a deep-off state, the small cell eNB doesnot transmit any signals including discovery signals, and the small celleNB is unable to monitor for uplink transmissions of UEs. In accordancewith some implementations, techniques or mechanisms are provided toawaken a small cell eNB from a deep-off state or other off state.

A sleeping small cell eNB (that is in a deep-off or off state) can beawakened in response to a wake command sent over the backhaul link 116,over the air, or over another link. Upon receiving the wake command, thesleeping small cell eNB can transition to a semi-off state or on state.The state that the sleeping small cell eNB should move to can beidentified in the wake command.

The wake command can be transmitted from one of the active small celleNBs (in the on state), or from another coordinating network node suchas the macro eNB 104. There can be several ways in which thecoordinating network node can determine if a sleeping small-cell eNBshould be awakened, and which of multiple deep-off small cell eNBs areto be awakened.

In some implementations, the determination of whether to awaken nearbysleeping small cell eNBs can be based on historical information, whichcan include fingerprint information collected during normal operation ofthe network. The fingerprint information can be used to identify anearby sleeping small cell eNB to awaken. More specifically, duringnormal operation (such as when both small cell eNBs SC-1 and SC-2 areactive), a UE (served by small cell eNB SC-2) can report backmeasurement information (e.g. a measurement vector), for each positionof the UE, indicating the quality of channels between the UE and each ofsmall cell eNBs SC-1 and SC-2 (and possibly other small-cell eNBs in theUE's range).

The reported measurement vector can change at different UE positions(the condition of each link depends on various factors includingphysical proximity of the UE to each eNB, fading coefficients, andenvironment obstacles). Based on the received measurement vectors, theserving small cell eNB SC-2 is able to monitor the quality of its linkto its associated UE, and if the link quality is not acceptable, theserving small cell eNB SC-2 can determine at the channel conditionbetween the UE and other small cell eNBs.

If appropriate (such as if the channel condition between the UE andanother small cell eNB is better than the channel condition between theUE and the small cell eNB SC-2), handover of the UE to another smallcell eNB (e.g. SC-1) can be performed. In the event of handover, thesmall cell eNB SC-2 can keep a record of the handover. For example, thesmall cell eNB SC-2 can store the corresponding measurement vector in adatabase and indicate that when a UE has such measurement vector (vectorV_1), it has been handed over to a specific small cell eNB (e.g. SC-1).This database can be updated during network operation; therefore, thedatabase can keep track of any structural modifications in the network.

The database can be used at the small cell eNB SC-2 to determine if thesmall cell eNB SC-2 should send a wake command to any neighboringsleeping small cell eNBs. Assume a network state in which the small celleNB SC-1 is in an off state, and a UE is connected to the small cell eNBSC-2. Now assume that the UE changes its position, and after the changein position, the UE sends a measurement report (e.g. measurement vectordiscussed above) to the small cell eNB SC-2.

In response to receiving a measurement vector, the small cell eNB SC-2can compare the measurement vector against the database maintained atthe small cell eNB SC-2. At some point in time, assume that the reportedmeasurement vector becomes closer to stored vector V_1 in the database,except for an entry of V_1 related to SC-1 (since SC-1 is sleeping, UE-1does not have any measurement for SC-1). If that happens, sincepreviously at this position, UE was handed over to SC-1 from SC-2, thesmall cell eNB SC-2 may decide to awaken the small cell eNB SC-1 fromthe off state to the semi-off or on state, such that the small cellsmall cell eNB SC-1 transmits discovery signals, so that the UE can alsomeasure and report the channel condition between the UE and SC-1. Otherfactors (e.g. loading of the serving small cell eNB SC-2) can also beused to decide if the small cell eNB SC-2 should send out a wake commandto its neighboring sleeping small cell eNBs.

Given the full measurement vector, the small cell eNB SC-2 can thendecide whether the small cell eNB SC-2 should hand over the UE to thesmall cell eNB SC-1.

The small cell eNB SC-1 that was awakened to the on or semi-off statecan wait for signaling from the UE. If the small cell eNB SC-1 does notreceive an uplink transmission from the UE within a specified timeperiod, the small cell eNB SC-1 can turn itself back to an off state.

Using techniques according to some implementations, the small cell eNBSC-2, can determine whether or not to awaken a neighboring sleepingsmall cell eNB without assistance from the macro eNB 104 (or othercoordinating node).

In further implementations, if there is a macro eNB 104 (or othercoordinating node) that can help determine UE locations or potentialneighboring small cell eNBs to awaken, the small cell eNB SC-2 can alsouse such information from the macro eNB 104 or other coordinating node.Any other rough estimation of a UE's location can also help to improvethe performance of deciding which neighboring sleeping small cell eNB toawaken.

In general, according to some implementations, a wireless access networknode collects information about network operation. The wireless accessnetwork node can use the collected information about network operationto decide whether or not to awaken a sleeping wireless access networknode. A wake command is then sent to the sleeping wireless accessnetwork node on a backhaul link.

The collected information can include information pertaining tohandovers of a UE, positions of the UE, and UE measurements.

When a small cell eNB is awakened, the small cell eNB can wait for aperiod of time and if the small cell eNB sees no new UE associationduring the period, the small cell eNB can again start a sleepingprocedure to transition to an off state.

Dynamic Power Control of a Small Cell eNB

In some implementations, a small cell eNB can be turned on and off in adynamic manner. For example, the small cell eNB can be turned on or offon a subframe-by-subframe basis, e.g. the small cell eNB can be turnedon in a first subframe (or first group of subframes) and turned off in asecond subframe (or second group of subframes) within a given systemframe.

The small cell eNB can dynamically turn on/off its transmission based onthe traffic or interference condition in the network. For example, ifthe small cell eNB has a UE to serve in a given subframe, the small celleNB will transmit data and/or control information in the given subframeto the UE. If the small cell eNB has no UE to serve in another subframe,then the small cell eNB can decide not to transmit data and controlinformation in the other subframe. For example, the small cell eNB candecide not to send a CRS or Channel State Information (CSI) referencesignal (CSI-RS) in the other subframe.

Implementing a dynamic small cell eNB on/off scheme may cause unwantedinterference. For example, when a UE is close to a small cell eNB, thesmall cell eNB may still transmit reference signals (such as CRS) atfull power to serve the UE, which may cause interference in neighboringcells.

To mitigate such interference, a dynamic power control technique can beapplied. With the dynamic power control technique, the small cell eNBcan dynamically control its transmit power on a subframe-by-subframebasis, even for transmitting CRS. For example, if a UE close to thesmall cell eNB is to be served in a first subframe, the small cell eNBcan transmit content in the first subframe at lower power level. If a UEfarther away from the small cell eNB is to be served in a secondsubframe, the small cell eNB can transmit to the UE at higher powerlevel.

It is noted that dynamic small cell on/off can be considered a specialcase of dynamic power control of a small cell eNB, because when thetransmit power from the small cell eNB is completely turned off, it isequivalent to dynamic small cell on/off.

In some implementations, the power levels of transmissions including CRSand other control signaling can be reduced in some subframes dependingon distribution of UEs that are to be served. A power level of atransmission can be determined based on feedback from a UE, where thefeedback can include RSRP, Reference Signal Received Quality (RSRQ), andChannel Quality Indication (CQI). For example, if the small cell eNB hasto schedule transmission in a given subframe only to a particular UE,the small cell eNB can adjust the transmission power level for the givensubframe based on the feedback from the particular UE. If there multipleUEs to be served in the given subframe, the transmission power can bedetermined based on the combined feedback from the multiple UEs.

Since a small cell eNB may not serve as many UEs as the macro eNB 104 ina given subframe, adjusting transmission power based on feedback fromthe UEs served by the small cell eNB can be feasible. In general, theprinciple is that the small cell eNB can serve UEs using a reducedamount of downlink transmission power (to reduce interference), whileensuring that the UEs can successfully receive information in each givensubframe. When there is no traffic scheduled in a given subframe, thesmall cell eNB can turn off its transceiver.

To support the ability to adjust transmission power on asubframe-by-subframe basis, the following are considered. A first issuerelates to measurements, such as Radio Resource Management (RRM) orRadio Link Monitoring (RLM) measurements. Another issue relates toChannel State Information (CSI) feedback.

According to E-UTRA, measurements such as RRM and RLM measurements relyon CRS, which is shared among multiple UEs. If the transmission power ofCRS changes from time to time, the RRM or RLM measurements may beimpacted. To resolve the impact on the measurements, the subframes canbe divided into two sets, as depicted in FIG. 12. The two sets include afirst set of subframes (hashed pattern boxes) and a second set ofsubframes (blank boxes).

In the first set of subframes, the small cell eNB can transmit normallyusing the power levels specified in current standards, and the powerlevels do not change rapidly over time. The first set of subframes canalso be used to transmit some common control information such assynchronization signals (e.g. PSS/SSS), CRS, system information, andpaging information. The UE can perform RRM and RLM measurements in thesesubframes. The CSI can be calculated in this first set of subframes aswell. Other operations, such as synchronization and synchronizationtracking, can also be performed using the first set of subframes. Tohandle interference between small cells in the first set of subframes,one of several solutions can be implemented.

A first solution is based on scheduling by the small cell eNB. The smallcell eNB can only schedule UEs that experience less interference, e.g.UEs closer to the center of the small cell, as determined frommeasurement information from UEs.

A second solution is based on coordinated transmission by small celleNBs. Small cell eNBs can coordinate their transmissions to reducemutual interference. For example, the small cell eNBs can coordinate thefrequency resources used in the first set of subframes. The coordinatingcan be performed based on communications over backhaul links between thesmall cell eNBs.

In the second set of subframes, a small cell eNB can perform dynamicpower control on a subframe-by-subframe basis (as discussed furtherabove). Legacy reference signals and control signals, such as CRS,Physical Control Format indicator Channel (PCFICH), Physical channelHybrid ARQ indicator Channel (PHICH), and Physical Downlink ControlChannel (PDCCH) may not be transmitted in the second set of subframes.

Backward compatibility issues may not appears if the dynamic powercontrol is only applied in the secondary cells. A small cell eNB thatsupports carrier aggregation can communicate over multiple componentcarriers of the carrier aggregation. One of the component carriers isconfigured as a primary cell while the remaining component carrier(s) is(are) configured as secondary cell(s). The primary cell is used tocommunicate certain control information to UEs served by the primarycell.

Legacy UEs (those that do not support a carrier of a new carrier type orNCT) can be served in backward compatible cells only. A new carrier type(NCT) refers to a carrier that is of a type different from a legacycarrier, where the new carrier type can be implemented to provide forenhanced features, including enhanced spectral efficiency, improvedenergy efficiency, improved support for heterogeneous networks, and soforth. A cell provided by a legacy carrier can be referred to as abackward compatible cell. A cell provided by an NCT carrier can be anNCT cell.

In a backward compatible cell, the CSI-RS, demodulation reference signal(DMRS), or Enhanced Physical Downlink Control Channel (EPDCCH) can beused for the purpose of data demodulation and measurement.

Alternatively, Multicast-Broadcast Single Frequency Network (MBSFN)subframes can be used where CRS and PDCCH are only transmitted in thefirst several OFDM symbols, while the rest of the symbols are used fortransmission of PDSCH using DMRS for demodulation. If the DMRS has thesame transmission power as PDSCH, no extra signal has to be used toinform the UE even if dynamic power control is applied on PDSCHtransmissions. The CRS transmission power level in a MBSFN subframe canalso be dynamically adjusted to reduce interference to other cells. Asthe CRS in this case is used for PDCCH decoding only and QuadraturePhase Shift Keying (QPSK) is used for PDCCH transmissions, the powerlevel of CRS does not have to be signaled to the UE.

To maintain the same interference level for RRM and RLM measurements,different small cell eNBs can use the same first set of subframes, wherethe CRS and other control signals are all transmitted at normal powerlevel. Thus, the RRM and RLM measurements can be accomplished in thefirst set subframes. For CSI measurement and feedback, it can also beconfigured and measured in the first set of subframes using CRS orCSI-RS because the transmit power levels of these signals are constant.The CSI measurement can be conducted in the second set of subframes.However, since the transmit signal power level including CSI-RS can varyfrom subframe to subframe, such CSI measurement may not be accurate.

The configuration of the two sets of subframes can be provided to UEs indedicated or broadcast RRC messages.

In general, according to some implementations, a wireless access networknode performs communications in a plurality of sets of subframes. In afirst set of subframes, the wireless access network node performsdynamic power control. In a second set of subframes, the wireless accessnetwork node does not perform dynamic power control.

The dynamic power control includes reducing a power level of a controlsignal on a subframe-by-subframe basis.

Reducing the power level of a transmission in a given subframe includesturning off the wireless access network node in the given subframe.

The configuration of the two sets of subframes can be provided to UEs indedicated or broadcast RRC messages.

System Architecture

FIG. 13 depicts a computing system 1300, which can be any of the macroeNB 104, small cell eNB 108, or other network node discussed above. Thecomputing system 1300 includes machine-readable instructions 1302, whichare executable on a processor (or multiple processors) 1304 to performvarious tasks discussed above. A processor can include a microprocessor,microcontroller, processor module or subsystem, programmable integratedcircuit, programmable gate array, or another control or computingdevice.

The processor(s) 1304 can be coupled to a communication interface (orcommunication component) 1306 to perform communications. For example,the communication interface 1306 can perform wireless communication overan air interface, or perform wired communication over a wiredconnection. In some cases, the computing system 1300 can includemultiple communication interfaces 1306 to communicate with respectivedifferent network nodes.

The processor(s) 1304 can also be coupled to a computer-readable ormachine-readable storage medium (or storage media) 1308, for storingdata and instructions. The storage medium or storage media 1608 caninclude one or multiple computer-readable or machine-readable storagemedia. The storage media include different forms of memory includingsemiconductor memory devices such as dynamic or static random accessmemories (DRAMs or SRAMs), erasable and programmable read-only memories(EPROMs), electrically erasable and programmable read-only memories(EEPROMs) and flash memories; magnetic disks such as fixed, floppy andremovable disks; other magnetic media including tape; optical media suchas compact disks (CDs) or digital video disks (DVDs); or other types ofstorage devices. Note that the instructions discussed above can beprovided on one computer-readable or machine-readable storage medium, oralternatively, can be provided on multiple computer-readable ormachine-readable storage media distributed in a large system havingpossibly plural nodes. Such computer-readable or machine-readablestorage medium or media is (are) considered to be part of an article (orarticle of manufacture). An article or article of manufacture can referto any manufactured single component or multiple components. The storagemedium or media can be located either in the machine running themachine-readable instructions, or located at a remote site from whichmachine-readable instructions can be downloaded over a network forexecution.

In the foregoing description, numerous details are set forth to providean understanding of the subject disclosed herein. However,implementations may be practiced without some of these details. Otherimplementations may include modifications and variations from thedetails discussed above. It is intended that the appended claims coversuch modifications and variations.

What is claimed is:
 1. A method comprising: receiving, by a userequipment (UE), information relating to a configuration for a discoverysignal for transmission by a first wireless access network node when thefirst wireless access network node is in an off state; receiving, by theUE from the first wireless access network node that is in the off state,the discovery signal according to the configuration; and detecting, bythe UE based on the received discovery signal, the first wireless accessnetwork node that is in the off state, wherein detecting, by the UE, thewireless access network node that is in the off state comprisesdetermining, by the UE, a cell identifier of the first wireless accessnetwork node that is in the off state.
 2. The method of claim 1, furthercomprising: sending, by the UE to a second wireless access network node,feedback information relating to the received discovery signal, thefeedback information causing the second wireless access network node tosend an indication to activate the first wireless access network nodefrom the off state to an on state.
 3. The method of claim 1, whereinreceiving the information relating to the configuration comprisesreceiving timing information for the discovery signal.
 4. The method ofclaim 1, wherein the configuration includes a signal configuration forthe discovery signal, the signal configuration specifying that thediscovery signal is a cell-specific signal.
 5. The method of claim 4,wherein the cell-specific signal is a signal selected from among acell-specific reference signal having an increased periodicity, and asynchronization signal having an increased periodicity.
 6. The method ofclaim 1, wherein the configuration includes a configuration relating toone or both a time resource and a frequency resource for carrying thediscovery signal.
 7. The method of claim 1, wherein the informationrelating to the configuration is received by the UE in a dedicated orbroadcast message.
 8. The method of claim 1, wherein the discoverysignal is derived from a sequence that is unique to the first wirelessaccess network node.
 9. The method of claim 8, wherein the sequence isorthogonal or quasi-orthogonal with respect to a sequence of a discoverysignal transmitted by another neighboring wireless access network node.10. The method of claim 8, wherein the sequence is based on a cellidentifier of a cell associated with the first wireless access networknode.
 11. The method of claim 1, wherein one or both of a sequence andresource of the discovery signal indicates a duplex mode of the firstwireless access network node.
 12. The method of claim 1, wherein thediscovery signal transmitted by the first wireless access network nodehas a same periodicity and is transmitted in a same resource as adiscovery signal transmitted by another wireless access network nodethat is in an off state, wherein the resource is one or more of a timeresource, a frequency resource, and a sequence resource.
 13. The methodof claim 1, wherein the discovery signal transmitted by the firstwireless access network node is carried in a different resource than aresource carrying a discovery signal transmitted by another wirelessaccess network node that is in an off state, wherein the differentresource is one or more of a time resource, a frequency resource, and asequence resource.
 14. A user equipment (UE) comprising: at least oneprocessor configured to: receive a Radio Resource Control (RRC) messagecontaining timing information pertaining to a discovery signal to betransmitted by a first wireless access network node in an off state;receive, from the first wireless access network node that is in the offstate, the discovery signal according to the timing information; anddetect, based on the received discovery signal, the first wirelessaccess network node that is in the off state, the detecting comprisingdetermining a cell identifier of the first wireless access network nodethat is in the off state.
 15. The UE of claim 14, wherein the timinginformation includes one or more of a periodicity of the discoverysignal and an offset of the discovery signal.
 16. The UE of claim 14,wherein a periodicity of the discovery signal is dynamically set and issent by a second wireless access network node to the first wirelessaccess network node.
 17. The UE of claim 14, wherein the RRC messagefurther contains one or more of a time resource and a frequency resourcefor the discovery signal.
 18. The UE of claim 14, wherein the at leastone processor is configured to further send, to a second wireless accessnetwork node, feedback information relating to the received discoverysignal, the feedback information causing the second wireless accessnetwork node to send an indication to activate the first wireless accessnetwork node from the off state to an on state.